Emissive display device

ABSTRACT

To obtain a paste for electron sources which can enhance heat resistance of carbon nanotubes, which can suppress burn-out of the carbon nanotubes even during heating at a high temperature, and can exhibit a high electron emission performance, boron (B) is added to the paste formed of the carbon nanotubes and metal. Due to the addition of boron, the oxidation of the carbon nanotubes can be suppressed, and the degradation of the electron emission characteristics and the degradation of the uniformity of the emission of electrons during the heating process such as baking can be prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paste for electron sources forforming electron sources which emit electrons upon applying of anelectric field, electron sources which use the paste for electronsources, and an emissive display device which forms the electron sourcesinto cathode lines.

2. Description of the Related Art

As a type of field emission panel display devices (FED), there has beenreported an emissive display device which uses inorganic carbonmaterials such as carbon nanotubes or carbon nanofibers as electronsources for emitting electrons upon applying of an electric field. Forexample, an example in which an emissive display device of a nominal 4.5inch is described in pp. 1134-1137 of SID99 Digest. The electron sourcesof this type are formed such that, for example, a paste for electronsources which is produced by mixing carbon nanotubes (CNT) and silver(Ag) particles (paste which is produced by mixing the carbon nanotubesin a silver paste) is applied to conductive films of cathode lines bycoating or printing and the paste is fixed to the conductive films byheating (baking) in the atmosphere.

However, when the inorganic carbon material paste formed of carbonnanotubes, carbon nanofibers in which silver is mixed is heated in theatmosphere at a temperature not less than 400 degree centigrade, theinorganic carbon material (also referred to as “carbon nanotubes or thelike” hereinafter) is oxidized due to a catalytic action of silver andis formed into CO₂ (or CO) so that a major portion of the material isdissipated. Accordingly, when the inorganic carbon material is used aselectron sources of a display device, the electron source cannot obtainthe sufficient electron emission characteristics and it is difficult toconstitute electron sources capable of uniformly emitting electrons.Further, the same tendency is recognized with respect to a pastecontaining other metal such as nickel (Ni) or the like other than silverto greater or lesser degrees.

Accordingly, with respect to the electron sources which are formed ofthe paste for electron sources which contains the carbon nanotubes orthe like and metal, it is necessary to perform heating such as baking ofa coating film or a printing film of the paste which is necessary in themanufacture of the display device at a temperature lower than an optimumtemperature which is generally necessary in the process or under thenon-oxidizing atmosphere. However, heating in the non-oxidizingatmosphere (atmosphere such as vacuum, nitrogen gas, argon gas or thelike) can hardly cope with the increase of size of the panel displaydevice due to restrictions imposed on process facilities including aheater. Further, also in baking the paste for electron sources in thenon-oxidizing atmosphere, the carbon nanotubes or the like are partiallydissipated due to a residual oxidizing gas or gasses generated from theprocess facilities and hence, the electron emission performance of theelectron sources is degraded and this also constitutes one of factorswhich make the emission of electrons non-uniform.

As a literature which discloses a technique for forming electron sourcesusing a paste for electron sources in which carbon nanotubes or the likeand silver are mixed (CNT-Ag paste), New Emitter Techniques for FieldEmission Displays written by J. M. Kim et al. (SID 01 DIGEST pp.304-307) is known. In this literature, the above-mentioned paste forelectron sources is subjected to screen printing, electron sources whichare baked at a temperature of 350 degree centigrade in the atmosphereare formed, and a substrate on which the electron sources are formed anda counter substrate on which phosphors and anodes are formed is heatedand sealed in an argon gas at a temperature of 415 degree centigrade.

SUMMARY OF THE INVENTION

The above-mentioned baking temperature 350 degree centigrade is a lowerlimit which decomposes organic binder components of the CNT-Ag paste andis set to such a value in view of the fact that heating at a temperaturenot less than 400 degree centigrade cannot perform in the atmosphere.However, it is desirable to perform baking at a higher temperature.Further, since a lower limit of the sealing temperature of the substrateis approximately 415 degree centigrade, the sealing is performed in thenon-oxidizing atmosphere such as an argon gas or the like.

However, to ensure the sufficient conductivity in a film or thesufficient film strength of the electron sources formed of the CNT-Agpaste, it is desirable to perform baking at a temperature not less than500 degree centigrade. Further, heating in the non-oxidizing atmospheresuch as an argon gas or the like cannot realize the complete preventionof the oxidation of the carbon nanotubes or the like and constitutes oneof factors which make the emission of electrons non-uniform.

Accordingly, it is an object of the present invention to provide a pastefor electron sources which can reduce the dissipation of carbonnanotubes or the like even in baking at a temperature of not less than400 degree centigrade. It is a further object of the present inventionto provide an electron source which is formed of such a paste forelectron sources. It is a still further object of the present inventionto provide an emissive display device which includes electron sourcesformed of such a paste for electron sources.

To achieve the above-mentioned objects, in the present invention, boron(B) is added to a paste formed of carbon nanotubes or the like andmetal. Due to an addition of boron, the oxidation of the carbonnanotubes or the like can be suppressed and hence, in a heating processsuch as baking or the like, it is possible to prevent the degradation ofthe electron emission characteristics and the degradation of the uniformelectron emission performance.

Boron to be added may be boron having high reducibility in a singleform, an alloy of boron or a boron oxide. The priority of oxidation isassigned to boron in a single form or an alloy of boron or the like perse and hence, the oxidation of carbon nanotubes or the like can beeffectively suppressed. On the other hand, boron oxide prevents theoxidation of the carbon nanotubes or the like as a protective layerwhich covers dangling bonds (surface defective edges) of the carbonnanotubes, for example. Further, the enhancement of oxidation resistanceof the carbon material by boron oxide is described in Japanese patent2749175 and “Chemistry and Physics of Carbon, volume 23”.

Further, since boron oxide is melted at a temperature of 450 degreecentigrade, it is also possible to obtain an advantageous effect thatthe carbon nanotubes or the like can be fixed to metal particles.Accordingly, it is possible to prevent the carbon nanotubes or the likefrom being peeled off from films of electron sources which are formed bycoating and baking a paste for electron sources containing the carbonnanotubes or the like and it is also possible to prevent the generationof discharge during an operation of panel display device using suchelectron sources. To the contrary, when the heat resistance treatment isnot applied to the carbon nanotubes or the like, the carbon nanotubes orthe like are burnt or are damaged in a heat treatment step of amanufacturing process of the display device thus giving rise a problemthat the electron emission characteristics of the carbon nanotubes orthe like is largely degraded. Typical constitutions of the presentinvention are enumerated hereinafter.

(1) At least metal, an alloy thereof, inorganic carbon material andboron (B) is contained in a paste for electron sources.

(2) Here, the above-mentioned boron is contained in at least one formselected from a group consisting of boron in a single form, a solidsolution of boron and other metal, an intermetallic compound of boronand other metal and a compound containing boron.

(3) Further, the above-mentioned boron is contained in at least one formselected from a group consisting of boron oxide, boric acid and alkoxideof boron.

(4) Further, the above-mentioned boron is contained in at least one formselected from a group consisting of boron in a single form, a solidsolution of boron and other metal, an intermetallic compound of boronand other metal and a compound containing boron, and in at least oneform selected from a group consisting of boron oxide, boric acid andalkoxide of boron.

(5) The above-mentioned intermetallic compound is at least one selectedfrom AgB₂, Ni₃B and Ni₂B.

(6) Further, the above-mentioned compound which contains boron is NaBH₄.

(7) A content of the above-mentioned boron is approximately 0.07 to 30,preferably 0.1 to 15, more preferably 0.4 to 15 as an atomic ratio withrespect to metal or alloy.

(8) A total quantity of the above-mentioned metal or alloy contained inthe above-mentioned paste for electron sources amounts to not less thanapproximately 50 volume % of a balance excluding organic components andinorganic carbon material contained in the paste for electron sources.

(9) Further, a total quantity of the above-mentioned inorganic carbonmaterial contained in the above-mentioned paste for electron sourcesamounts to approximately 0.1 to 9 as an atomic ratio with respect to atotal quantity of the above-mentioned metal and alloy contained in thepaste for electron sources.

(10) The above-mentioned inorganic carbon components contained in theabove-mentioned paste for electron sources include at least one ofcarbon nanotubes or carbon nanofibers.

(11) Further, a content of the above-mentioned carbon nanotubes orcarbon nanofibers is approximately not less than 1%, preferably not lessthan 10% as a weight % with respect to a total quantity of theabove-mentioned inorganic carbon components contained in theabove-mentioned paste for electron sources.

(12) As the above-mentioned metal or alloy contained in theabove-mentioned paste for electron sources, at least one selected from agroup consisting of silver (Ag), nickel (Ni), gold (Au), aluminum (Al),iron (Fe), copper (Cu), zinc (Zn), palladium (Pd), tungsten (W),molybdenum (Mo), tantalum (Ta), titanium (Ti), chromium (Cr) and iridium(Ir) is contained in the paste for electron sources.

(13) As the above-mentioned metal or alloy which is contained in theabove-mentioned paste for electron sources, the metal or the alloy whichcontains at least one of Ag or Ni as a main component is used.

(14) An electron source is obtained by coating or printing theabove-mentioned paste for electron sources and by heating the paste forelectron sources at a temperature not less than approximately 400 degreecentigrade, more preferably at temperature of not less than 450 degreecentigrade so as to fix the paste for electron sources.

(15) In an emissive display device which includes cathode lines, controlelectrodes and anodes having phosphors, the self-luminous panel displaydevice is further provided with the above-mentioned electron sources asthe cathode lines.

In the above-mentioned paste for electron sources, by adding boron tothe carbon nanotubes and the silverpaste (CNT-Ag paste), for example, itis possible to suppress the dissipation of the carbon nanotubes byoxidation. With respect to boron which has the strong reducibility, thepriority of oxidation is assigned to boron per se so that the oxidationof the carbon nanotubes can be suppressed. Boron oxide covers danglingbonds of the carbon nanotubes so as to suppress the oxidation of thecarbon nanotubes. Accordingly, even when the carbon nanotubes aresubjected to the heating process at a temperature not less than 400degree centigrade in the atmosphere, the carbon nanotubes are notdissipated and hence, it is possible to obtain the sufficient electronemission characteristics.

Further, by adopting heating in the non-oxidizing atmosphere along withthe use of boron in combination, an allowable range of a residualoxidizing gas and generating gases is large and hence, the localoxidation of the carbon nanotubes can be also prevented whereby theuniformity of the emission of electrons can be improved particularly.

Further, boron oxide is melted at a temperature of 450 degree centigradeand plays a role of fixing the carbon nanotubes to metal particles andhence, it is possible to prevent the carbon nanotubes from being peeledoff from films of the formed electron sources so that the generation ofdischarge can be obviated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view for explaining the electric fielddependency of an emission current density which is indicated by graphsin which a change of electron emission characteristics of an Ag-CNTpaste due to heating conditions and a change of similar electronemission characteristics of an Ag-CNT paste in which boron is added areplotted.

FIG. 2A and FIG. 2B are scanning electron microscope photographs offilms of electron sources which are obtained by baking respectively theAg-CNT paste and the Ag-B-CNT paste in the atmosphere at a temperatureof 590 degree centigrade.

FIG. 3 is an explanatory view for explaining the boron quantitydependency of an electric field of the Ag-B-CNT paste necessary foremitting electrons.

FIG. 4 is a scanning electron microscope photograph showing a surface ofan electron source film (Ag-B-CNT film) after baking the Ag-B-CNT pastein the atmosphere at a temperature of 590 degree centigrade twice.

FIG. 5A and FIG. 5B are scanning electron microscope photographs forcomparing surfaces of Ni-CNT and Ni-B-CNT after heating them at atemperature of 590 degree centigrade in the atmosphere.

FIG. 6 is a developed perspective view of an essential part forexplaining a constitutional example of an electric field emissiondisplay device according to the present invention.

FIG. 7 is a schematic perspective view for explaining an example of aholding structure for holding an electron-source side substrate and aphosphor-screen side substrate at a given distance.

FIG. 8 is an equivalent circuit for explaining one example of a drivingmethod of the display device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are explained in detailhereinafter in conjunction with drawings showing the embodiments. Anexample in which carbon nanotubes are used as an inorganic carbonmaterial is explained hereinafter. A mixture obtained by mixing thecarbon nanotubes in a silver paste is applied to a substrate by coatingand, thereafter, the mixture is fixed by heating (baking) thus formingelectron sources of a field emission type panel display device (FED). Insuch a manufacturing process, silver particles having an averageparticle size of 1 to 3 μm and the carbon nanotubes (including graphiteand amorphous carbon or the like) are mixed together with acellulose-based binder, a dispersing agent, additives and the like thuspreparing a paste for electron sources.

Here, an Ag-CNT paste is prepared by adjusting an atomic ratio (C/Ag) ofa quantity of inorganic carbon components (C: carbon nanotubes,graphite, amorphous carbon or the like) to silver to 1.8 (C/Ag, weightratio 0.2). Here, as a material of the carbon nanotubes, multi-wall CNTwhich is manufactured by an arc discharge method in a rare gas is used.

FIG. 1 is an explanatory view for explaining the electric fielddependency of an emission current density which is indicated by graphsin which a change of electron emission characteristics of an Ag-CNTpaste due to heating conditions and a change of similar electronemission characteristics of an Ag-CNT paste in which boron is added areplotted, wherein an electric field intensity (V/μm) is taken on an axisof abscissas and an emission current density (mA/cm²) is taken on anaxis of ordinates. In the drawing, a graph indicated by a white triangle

shows a case in which the Ag-CNT paste is baked in the atmosphere at atemperature of 350 degree centigrade, a graph indicated by a whitecircle ◯ shows a case in which the Ag-CNT paste is baked in theatmosphere at a temperature of 450 degree centigrade, a graph indicatedby a white square

shows a case in which the Ag-CNT paste is baked in the atmosphere at atemperature of 590 degree centigrade, a graph indicated by a blacksquare ▪ shows a case in which the Ag-CNT paste is baked in theatmosphere at a temperature of 590 degree centigrade, and a graphindicated by a white star ⋆ shows a case in which the Ag-B-CNT paste isbaked in the atmosphere at a temperature of 590 degree centigrade.

To achieve these graphs, the Ag-CNT paste having a large film thicknessis printed on a surface of a glass substrate within a region of 3 by 3mm square and is baked respectively at a temperature of 350 degreecentigrade, 450 degree centigrade and 590 degree centigrade in theatmosphere to produce baked films which constitute samples. An anode isarranged in front of the baked film which constitutes the sample with adistance of 400 μm therebetween and the electron emissioncharacteristics are measured.

As shown in respective graphs indicated by the white triangle

, the white circle ◯ and the white square

, the higher the baking temperature, an electric field necessary foremission of electrons is increased (the emission of electron becomesmore difficult), and the emission of electrons can not be obtained evenwith a high electric field having an electric field intensity of 8V/μmin baking at a temperature of 590 degree centigrade. However, when thesame paste is baked in the nitrogen atmosphere at a temperature of 590degree centigrade, the emission of electrons of approximately 20 mA/cmis obtained at an electric field intensity of approximately 4 V/μm.

The reason that the sufficient emission of electrons is not obtained orthe emission of electron is not obtained at all in the atmosphere at ahigh temperature is that due to heating in the oxidizing atmosphere,carbon such as carbon nanotubes or the like are oxidized and dissipatedin a form of carbonic acid gas. However, when only the carbon nanotubeswhich are used in the paste are heated at a temperature of 600 degreecentigrade, the carbon nanotubes are hardly dissipated by burning. Thisis because that silver works as an oxidation catalyst and promotes theoxidation of the carbon nanotubes. Accordingly, unless the paste of thecarbon nanotubes does not contain Ag (or other metal having an oxidationcatalytic action), the carbon nanotubes can withstand the heating in theatmosphere at not less than 400 degree centigrade.

However, from a viewpoint of ensuring the conductivity of the electronsource using the carbon nanotubes (CNT) and a film strength of theelectron source, it is desirable that Ag (Ag particles or other metalparticles) is contained in the paste of the carbon nanotubes. Further,even in the paste of the carbon nanotubes containing metal which acts asan oxidation catalyst, it is possible to suppress the oxidation of thecarbon nanotubes provided that heating is performed in the nitrogenatmosphere (or other non-oxidizing atmosphere). However, it is notappropriate to realize the above-mentioned baking treatment in such anon-oxidizing atmosphere in the manufacturing process of a large-sizedsubstrate of a nominal diagonal 40 inch class.

The fact that metal which has an oxidation catalytic action such as Agpromotes the oxidation (burn-out) of the carbon nanotubes is common inall carbon-based materials and a similar oxidation promoting phenomenonis observed with respect to multi-wall CNT, single-wall CNT, graphite,diamond-like carbon, amorphous carbon and the like. As a technique whichprevents the oxidation of carbon, a technique to cover dangling bonds ona surface of carbon with B-O (boron-oxygen) is described inJP1991-271184A and page 208, Third chapter, Volume 23 of Chemistry andPhysics of Carbon.

Embodiments of the present invention are explained hereinafter in viewof the above fact.

[Embodiment 1]

An Ag-B-CNT paste is prepared by adding boron B to an Ag-CNT paste suchthat an atomic ratio B/Ag becomes 0.8 (B/Ag weight ratio: 0.08). Here,the atomic ratio means a ratio between the numbers of respective atoms.Boron in a single form is used as a boron adding material. When theAg-B-CNT paste is heated (baked) in the atmosphere at a temperature of590 degree centigrade, as indicated by the white star in FIG. 1, theemission of electrons of 20 mA/cm is obtained at an electric fieldintensity of approximately 3V/μm. In this manner, when boron is added,it is possible to realize the emission of electrons even when the pasteis heated in the atmosphere at a temperature of 590 degree centigradeand, at the same time, the further enhanced electron emissioncharacteristics can be obtained compared to a case that an Ag-CNT pasteto which boron is not added is heated in an nitrogen atmosphere.

FIG. 2A and FIG. 2B are scanning electron microscope photographs offilms of electron sources which are obtained by respectively baking anAg-CNT paste and an Ag-B-CNT paste in the atmosphere at a temperature of590 degree centigrade. That is, FIG. 2A is a baked film of the Ag-CNTpaste and FIG. 2B is a baked film of the Ag-B-CNT paste. In FIG. 2A,carbon nanotubes are dissipated and only silver particles remain.Portions formed in a cocoon shape in FIG. 2A are silver (Ag) particles.To the contrary, in FIG. 2B, carbon nanotubes CNT which remain withoutbeing oxidized are present between silver particles. In FIG. 2B. thecarbon nanotubes (CNT) having a fiber shape are observed. Here, in FIG.2B, boron oxide (B₂O₃) is present such that the boron oxide connects thecocoon-shaped silver (Ag) particles.

Experiments similar to this embodiment are performed with respect toAg-CNT which uses single-wall CNT and multi-wall CNT prepared by athermal CVD method. Also in these experiments, it is confirmed that theoxidation and the burn-out of the carbon nanotubes can be suppressed bythe addition of boron and the favorable electron emissioncharacteristics can be obtained even with heating in the atmosphere.

[Experiment 2]

FIG. 3 is an explanatory view for explaining the boron quantitydependency of an electric field of the Ag-B-CNT paste necessary foremitting electrons. In FIG. 3, the Ag-B-CNT pastes are prepared bychanging a quantity of boron B within a range of 0.05 to 50 as an atomicratio of B/Ag (B/Ag weight ratio: 0.005 to 5). A case in which boron ina single form is used as a boron adding material and a case in whichboron oxide (B₂O₃) is used as a boron adding material are indicated.Printing films formed of these pastes for electron sources are heated(baked) in the atmosphere at a temperature of 590 degree centigrade and,thereafter, electric fields which can obtain the emission of electronsof 20 mA/cm² are measured. A result of the measurement is shown in FIG.3.

When boron in a single form is added, the emission of electrons isobtained at an electric field having an electric field intensity of notmore than 8V/μm when the B/Ag atomic ratio falls in a range of 0.07 to30 and the emission of electrons is not observed except for this rangeeven when the electric field intensity is 10V/μm (see a solid line a inFIG. 3). This implies that when an addition quantity of boron is small,the anti-oxidation and protective effect become insufficient, while whenan addition quantity of boron is excessively large, boron excessivelycovers a surface of a film and hence, the electron emissioncharacteristics is lowered. When boron oxide is used as the boron addingmaterial, the emission of electrons is obtained when the B/Ag atomicratio falls in a range of 0.35 to 30 (see a broken line b in FIG. 3).From these results, it is understood that the boron adding effect can beobtained at least in these composition ranges (B/Ag atomic ratio).

Here, in a field emission type panel display device (FED), it ispreferable that a driving voltage which is served for allowing electronsources to generate electrons is as small as possible and the drivingvoltage of not more than approximately 150V is desirable. Provided thatthe driving voltage is held at such a level, an existing driving circuitwhich can be obtained at a low cost is available. Here, when en electronsource made of carbon nanotubes which is formed by printing is used, adistance from the electron source to a gate electrode for pulling outelectrons is approximately 25 μm. (It is difficult to form or arrangethe electron source with accuracy when the distance is below 25 μm.)

Accordingly, to set the driving voltage to a value not more than 150V,it is necessary to obtain a desired electric current density at anelectric field having an electric field density of not more than 6V/μm(=150V/25 μm). The required electric current density must be 5 to 10mA/cm as an electric current density on a phosphor screen from aviewpoint of light emission luminance. However, in view of the necessityto build up a gate electrode structure, an effective electron sourcearea is restricted to not more than one half of a substrate on which theelectron sources are formed. Therefore, it is necessary to ensure theelectric current density of 10 to 20 mA/cm at the electron sources.Accordingly, as the characteristics of the electron sources which usethe carbon nanotubes, it is desirable that the electric current densityof approximately 20 mA/cm is obtained in the electric field having anelectric field intensity of not more than 6 V/μm. The composition rangein which this characteristics can be obtained is approximately 0.1 to 15as the atomic ratio of B/Ag when boron is added in a single form and isapproximately 0.4 to 15 as the atomic ratio of B/Ag when boron is addedin a form of boron oxide.

The reason that boron in a single form has a larger oxidation preventioneffect than boron oxide even at a low concentration is attributed to adouble protective effect that boron in a single form exhibits. That is,boron in a single form per se is preferentially oxidized compared tocarbon so that the oxidation of the carbon nanotubes is suppressed. Atthe same time, boron is formed into boron oxide and is absorbed into asurface of carbon nanotubes thus forming a protective layer.

However, boron (in a single form) is easily oxidized and hashygroscopicity and hence, even when boron is added into the paste asboron in a single form, there is a high possibility that some boronoxide (or boric acid) is present in the paste in a strict sense so thatthere arises irregularities in the boron addition effect. Accordingly,to surely achieve the reliable reproducibility of the boron additioneffect in the application of boron to the electron source for FED, evenwhen boron is added in a single form, it is preferable to adjust thecomposition range to 0.4 to 15 as the atomic ratio of B/Ag when boron isadded as boron oxide.

When the intermetallic compound with silver, hydroxide boron sodium(NaBH₄), boric acid (H₃BO₃) or alkoxide such as B(OCH₃)₃ is used as theboron adding material, it is possible to obtain electron emissioncharacteristics equal to the electron emission characteristics of boronin a single form or of boron oxide, or the intermediate electronemission characteristics thereof. With respect to the intermetalliccompound and the hydroxide boron sodium, in the same manner as boron perse, first of all, boron per se in these compounds is oxidized so as tosuppress the oxidation of the carbon nanotubes and, thereafter, boron isformed into boron oxide to form a protective layer which covers thecarbon nanotubes. Boric acid and alkoxide are decomposed and are formedinto boron oxide by heating and perform functions in the same manner asthe case where boron oxide is added.

FIG. 4 is a scanning electron microscope photograph of a surface of anelectron source film (Ag-B-CNT film) after baking an Ag-B-CNT pastetwice in the atmosphere at a temperature of 590 degree centigrade. Whenthe carbon nanotubes (CNT) are protected with boron oxide once, evenwhen the paste is subjected to heating in the atmosphere again, boronoxide maintains a protective effect. In the scanning electron microscopephotograph of the Ag-B-CNT film obtained after performing heating againin the atmosphere at a temperature of 590 degree centigrade, the carbonnanotubes are explicitly observed in a fiber pattern in the drawing.Further, the degradation of the electron emission characteristics cannotbe also observed. This implies that the Ag-B-CNT paste exhibitsresistance not only in the baking process of the printing paste but alsoin the heating process of manufacturing of the FED panel which followsthe baking process. Accordingly, it is possible to expect the remarkableenhancement of a yield rate of the panel manufacturing and thereliability of products.

[Embodiment 3]

FIG. 5A and FIG. 5B are scanning electron microscope photographs servedfor comparing surfaces of an Ni-CNT paste and an Ni-B-CNT paste afterbaking them in the atmosphere at a temperature of 590 degree centigrade.That is, FIG. 5A is a baked film of the Ni-CNT paste and FIG. 5B is abaked film of the Ni-B-CNT paste. The Ni-B-CNT paste is prepared in thesame manner as the embodiment 1. Nickel (Ni) having an average particlesize of approximately 1 μm is used and the compound ranges arerespectively adjusted to an atomic ratio of 1.2 (weight ratio: 0.25) asC/Ni and to an atomic ratio of 0.45(weight ratio 0.09) as B/Ni. TheNi-B-CNT paste and the Ni-CNT paste which does not contain boron areheated (baked) in the atmosphere at a temperature of 590 degreecentigrade. As a result, with respect to the Ni-B-CNT paste, it isconfirmed that carbon nanotubes (CNT) remain in a fiber pattern as shownin FIG. 5B. Accordingly, in the same manner as the paste which uses thesilver particles, the paste which uses nickel particles can prevent theoxidation of the carbon nanotubes by the addition of boron.

In general, metal and oxide thereof function as oxidation catalysts inmany cases. Accordingly, in a paste in which other metal and carbonnanotubes (or other inorganic carbon component) are mixed, boronperforms the similar advantageous effect. According to a result obtainedby reviewing gold (Au), aluminum (Al), iron (Fe), copper (Cu), zinc(Zn), palladium (Pd), tungsten (W), molybdenum (Mo), tantalum (Ta),titanium (Ti), chromium (Cr) and iridium (Ir), boron exhibits a similaradvantageous effect as in the case of silver and nickel. Further, it isalso evident that a similar advantageous effect can be obtained whenthese metals are used in mixture.

FIG. 6 is a developed perspective view of an essential part forexplaining a constitutional example of an electric field type displaydevice according to the present invention. In the drawing, numeral 1indicates an electron-source side substrate, numeral 2 indicateselectron source lines (cathode lines), numeral 3 indicates electronsources formed of Ag-B-CNT, numeral 4 indicates metal grids (controlelectrodes), numeral 5 indicates opening portions (electron passingholes) formed in the metal grid electrodes, and numeral 6 indicates aphosphor-screen side substrate which is provided with anodes andphosphors on an inner surface thereof. In this embodiment, the Ag-B-CNTpaste of the example 1 is used. First of all, the electron source lines2 are formed on the electron-source side substrate 1 by printing andbaking the silver paste. The Ag-B-CNT paste which constitutes theelectron sources is printed on upper surfaces of the electron-sourcelines 2. The Ag-B-CNT paste is baked in the atmosphere at a temperatureof 590 degree centigrade to form the electron sources and, thereafter,the metal grid electrodes 4 which have the opening portions 5 arearranged in an overlapped manner.

Glass frit (not shown in the drawing) is used for fixing the gridelectrodes 4 to the inner surface of the electron-source side substrate1. For fixing the metal grid electrodes 4 using this glass frit, heatingis performed in the atmosphere at a temperature of 450 degreecentigrade. A distance between lower ends of the opening portions 5 ofthe metal grid electrodes 4 and a surface of the Ag-B-CNT is set toapproximately 25 μm.

Further, FIG. 7 is a schematic perspective view for explaining oneexample of the holding structure for holding a distance between theelectron-source side substrate 1 and the phosphor-screen side substrate6 at a given one. Partition walls (or spacers) 7 are interposed betweenthe electron-source side substrate 1 on which the above-mentionedelectron source lines 2, the electron sources 3 and the metal gridelectrodes 4 are formed and the phosphor-screen side substrate 6, andperipheries of both substrates 1, 6 are sealed by a glass frame (notshown in the drawing) and glass frit (not shown in the drawing). Thissealing is performed in the atmosphere at a temperature of 430 degreecentigrade. Thereafter, a space defined between both substrates 1, 6 isevacuated while being heated at a temperature of 350 degree centigradeand is held in vacuum by sealing.

FIG. 8 is an equivalent circuit for explaining one example of a drivingmethod of the display device according to the present invention. In thisdisplay device, n pieces of electron source lines (cathode lines) 2which extend in the y direction are arranged in parallel in the xdirection. Further, m pieces of control electrodes (metal grids) 4 whichextend in the x direction are arranged in parallel in the y directionthus constituting a matrix of m lines x n columns together with thecathode lines 2.

A scanning circuit 60 and a video signal circuit 50 are arranged in theperiphery of the electron-source side substrate which constitutes thedisplay device. Respective control electrodes 4 are connected to thescanning circuit 60 through control electrode terminals 40 (Y1, Y2, . .. Ym). Then, respective cathode lines 2 are connected to the videosignal circuit 50 through cathode terminals 20 (X1, X2, . . . Xn).

For each pixel at the crossing portions of the cathode lines 2 and thecontrol electrodes 4 which are arranged in a matrix array, any one ofelectron sources which are formed by coating and baking the carbonnanotube paste containing boron which has been explained in the previousembodiments is provided. Here, in the above-mentioned embodiment,although the explanation has been made such that one electrode source isprovided for one pixel in each cross section, the number of pixels isnot limited to the above case. That is, two or more pixels can bearranged within one pixel region. R, G, B in the drawing are monochroicpixels of red (R), green (G), blue (B) which respectively constituterespective color pixels, wherein lights corresponding to respectivecolors are emitted from phosphors.

Various types of signals for display are applied to the scanning circuit60 and the video signal circuit 50 from a host computer not shown in thedrawing. Synchronous signals 61 are inputted to the scanning circuit 60.The scanning circuit 60 selects a line of the matrix of the controlelectrodes 4 through the control electrode terminals 40 and applies ascanning signal voltage to the selected control electrode 4.

On the other hand, video signals 51 are inputted to the video signalcircuit 50. The video signal circuit 50 is connected to the cathodelines 2 through cathode terminals 20 (X1, X2, . . . Xn), a column of thematrix is selected and then a voltage corresponding to the video signal51 is applied to the selected cathode line. Accordingly, given pixelswhich are sequentially selected by the control electrodes 4 and thecathode lines 2 emit lights of given colors so as to display atwo-dimensional image.

With the use of the display device which adopts the carbon nanotubesaccording to this embodiment as electron sources, it is possible torealize a bright FED display device which is operated at a relativelylow voltage and with high efficiency without display irregularities.

As has been described above, the Ag-B-CNT paste of this embodiment canbe baked in the atmosphere at a sufficiently high temperature (590degree centigrade) and hence, the electron sources 3 formed of Ag-B-CNThave a sufficient strength and the sufficient conductivity. Further,even when the Ag-B-CNT paste is subjected to the subsequent heatingprocess, there is no possibility that the carbon nanotubes are oxidized(burn out) and hence, it is possible to obtain the sufficient emissionof electrons. In this FED display device, when 7 kV is applied to theanodes formed on the inner surface of the phosphor-screen side substrate6 and the FED display device is operated with a grid voltage of 100V(driving at 60 Hz), the luminance of 500 cd/m² which is sufficient forthis type of display device is obtained.

To the contrary, when the display device is prepared by the samemanufacturing process as described above using the conventional Ag-CNTpaste, the emission of light is hardly obtained. With respect to theAg-CNT paste, to suppress the oxidation of the carbon nanotubes, a casein which the baking temperature of the paste is set to 350 degreecentigrade is also tested. Also in this case, since the Ag-CNT paste hasto pass another heating process which is performed at a temperature of450 degree centigrade and hence, the electron source film is degradedwhereby the luminance is approximately one half of the luminance whichis obtained when the Ag-B-CNT paste is used under the same drivingconditions. Further, although all heating processes in the manufacturingof FED are performed using a device which can replace the atmospherewith the nitrogen atmosphere, the luminance is apparently reducedcompared to a case in which the display device is prepared through theheating process in the atmosphere using the Ag-B-CNT paste. Thissuggests that in the heating processes for assembling the FED, thegeneration of gasses from respective constitutional materials and themanufacturing equipment or jigs is unavoidable and hence, it isdifficult to maintain the complete non-oxidizing atmosphere.

Here, in a case that the Ag-B-CNT paste is used as the electron sources,when the baking and the succeeding heating process are performed in thenitrogen atmosphere, a phenomenon in which the uniformity of emission oflight is further enhanced is obtained. This may be attributed to a factthat the carbon nanotube protection effect brought about by the additionof boron and the protection effect brought about by heating under thenon-oxidizing atmosphere are superposed and hence, it was possible tosuppress not only the macroscopic oxidation and burn-out of the carbonnanotubes but also the microscopic local oxidation of the surface ofcarbon nanotubes.

In this manner, when the Ag-B-CNT paste of this embodiment is used forproducing the electron sources, it is possible to manufacture the FEDhaving the sufficient performance even during the heating processes inthe atmosphere and hence, it is possible to provide the display devicehaving high quality at a low cost. Further, by using this provision incombination with the heating process under the non-oxidizing atmospheresuch as nitrogen, the uniformity of emission of light is furtherenhanced. Accordingly, it is possible to realize a display exhibitinghigh definition and high display quality.

Here, the execution of the heating process in the completelynon-oxidizing atmosphere which is considered as an alternative for acase in which boron is not added is extremely difficult due to gassesgenerated from the constitutional members. Accordingly, it is reasonableto state that the addition of boron into the electron sources using thecarbon nanotubes is inevitable in the FED technique which uses thecarbon nanotubes as the electron sources. The present invention includesnot only the paste for electron sources which includes boron but alsothe electron sources which are manufactured using the paste and thedisplay device provided with these electron sources.

Further, although it is a socondary effect, according to the presentinvention, an advantageous effect that an inner discharge of the FEDdisplay device is prevented is obtained. The reason is considered thatboron oxide is melted at a temperature of approximately 450 degreecentigrade and hence, the carbon nanotubes and the metal particles arefixed to each other. Accordingly, the rupture of panel attributed todischarge can be suppressed so that the reliability of the FED displaydevice is enhanced.

Here, in the above-mentioned embodiments of the present invention, thecase in which the carbon nanotubes CNT (multi-wall CNT and single-wallCNT, also including carbon nanofibers in a broad definition) is used asthe electron emission material has been explained. However, the presentinvention can obtain the same advantageous effects so long as theelectron emission material is an inorganic carbon material. As theinorganic carbon material other than carbon nanotubes, for example,diamond, diamond-like carbon, graphite or amorphous carbon can be used.The mixture of these materials can be also used as the electron emissionmaterial. However, the carbon nanotubes are the excellent electronemission material among the carbon materials and hence, it is preferablethat the carbon nanotubes amount to not less than 1%, preferably notless than 10% in the inorganic carbon components.

Further, the metal paste contains an inorganic binder such as glassbesides metal in many cases. However, in this case, to make the metalpaste exhibit the sufficient conductivity, the composition of metalpaste is adjusted in general such that metal occupies not less than onehalf of the volume of the metal/inorganic binder composition. Also inthe present invention, it is preferable that a quantity of metalcomponent is larger than a quantity of inorganic binder component.

Further, in the embodiment of the present invention, a step in whichboron was adds after preparation of a mixed paste of metal and carbonnanotubes is adopted to add boron. However, it is needless to say thatthe metal component is added after preliminarily performing the mixingtreatment of boron with the carbon nanotubes and the inorganic carboncomponent, or all of these components are simultaneously mixed with eachother.

Further, it is needless to say that the present invention is not limitedto the constitution of the above-mentioned embodiments, the subject towhich the present invention is applicable is not limited to the FED andvarious modifications can be made within a scope of the technicalconcept of the present invention.

As has been explained heretofore, according to the present invention,the heat resistance of the paste in which the carbon nanotubes are mixedcan be enhanced with the addition of boron. Particularly, it is notnecessary to perform the electron-source baking step and the substratesealing step in the manufacturing process of the FED in thenon-oxidizing atmosphere and hence, it is possible to use a generalheating furnace (or a baking furnace) whereby the reduction of amanufacturing cost can be achieved. Further, by adopting heating orbaking in the non-oxidizing atmosphere in combination with the additionof boron, the uniformity of emission of electrons can be furtherenhanced so that it is possible to provide the display device of highquality. Further, since a high voltage is applied to the phosphor screenin the FED, when the carbon nanotubes are scattered and are adhered toportions other than given positions, this may generate a discharge andthere is a possibility that the display device receives a damage.According to the electron sources of the present invention, since thecarbon nanotubes are hardly scattered and hence, such a possibility canbe drastically reduced thus enhancing the reliability of the displaydevice.

1-14. (canceled)
 15. A display device comprising: cathode lines havingan electron source film, control electrodes and an anode havingphosphors, wherein the electron source film includes a metal particle ora particle of an alloy thereof, inorganic carbon material which is anelectron source, and boron (B), and the boron is contained in at leastone form selected from the group consisting of boron in a single form, asolid solution of boron and another metal, an inter-metallic compound ofboron and another metal and a compound containing boron.
 16. A displaydevice according to claim 15, wherein the inorganic carbon materialincludes carbon nanotubes or carbon nanofibers.
 17. A display deviceaccording to claim 15, wherein the inter-metallic compound includessilver boride (AgB₂) or nickel boride (Ni₃B or Ni₂B).
 18. A displaydevice according to claim 16, wherein the inter-metallic compoundincludes silver boride (AgB₂) or nickel boride (Ni₃B or Ni₂B).
 19. Adisplay device according to claim 16, wherein a content of the carbonnanotubes or the carbon nanofibers is approximately not less than 1% byweight with respect to a total quantity of the inorganic carbonmaterial.
 20. A display device according to claim 15, wherein the metalor the alloy includes at least one element selected from a groupconsisting of Ag, Ni, Au, Al, Fe, Cu, Zn, Pd, W, Mo, Ta, Ti, Cr and Ir.21. A display device according to claim 16, wherein the metal or thealloy includes at least one element selected from a group consisting ofAg, Ni, Au, Al, Fe, Cu, Zn, Pd, W, Mo, Ta, Ti, Cr and Ir.
 22. A displaydevice according to claim 15, wherein the metal or the alloy contains atleast one of Ag or Ni as a main component.
 23. A display deviceaccording to claim 16, wherein the metal or the alloy contains at leastone of Ag or Ni as a main component.